Electrical wrench



May 21, 1968 N. c. DAHL ELECTRICAL WRENCH Filed July 24, 1967 INVENTOR. NORMAN C. DAHL. BY

ATTORNEY FIG. 3

United States Patent 3,383,961 ELECTRICAL WRENCH Norman C. .Dahl, 40 Fern St., Lexington, Mass.

Filed July 24, 1967, Ser. No. 655,546 6 Claims. (Cl. 81-52.4)

ABSTRACT OF THE DISCLOSURE Background of the inventi0n.-This invention relates to a wrench or tightening device which is used in combination with and is electrically responsive to a stress indicating fastener such as a nut or bolt.

In tightening nuts and bolts to abutting surfaces, it is always desirable to tighten the bolt until the load, it was designed to carry, is reached. To determine when the design load is reached, several methods are used, such as, torque wrenches, bolts which elongate slightly, compressible washers, or nuts and bolts which elastically or plastically deform or change color when the design load is reached.

The torque wrench is unacceptable in that the measurement is subject to variations in friction factors. The other methods although they measure stress directly require instruments or visual checks to determine when the design load is reached. This is particularly disadvantageous when the wrenching means is engaged with the surface in which is incorporated the stress indicating means. In this instance, the wrench must be removed periodically to determine if the design load has been reached.

Summary of the inventi0n.l have discovered a new and unique apparatus and method in which a wrench engages the surface of a bolt or nut, which wrench is electrically responsive to the elastic or plastic deformation of the surface with which it is engaged. The wrench essentially incorporates within the jaw a contact point for an electric circuit. For the purposes of this application, the term jaw refers to that portion of the wrench which grippingly engages the nut or bolt in order to tighten the nut or bolt. This contact point is adjacent the surface of the bolt or nut so that upon deformation of the nut or bolt the contact is touched and the circuit closed. The closing of the circuit by the deformation of the fastening member may be caused by either the movement of the fastening member or by the extrusion of an electrically conducting material from the member such as described in my copending application, Ser. No. 655,112, filed July 21, 1967. The contact point in the jaw is connected to an electrical circuit.

The electric circuit can be mounted on the wrench in the case of a hand wrench or in the case of a power tool it may be incorporated within the body of the tool.

It is obvious that various arrangements for tying in an electrical circuit are possible and correspondingly, any type of signal can be incorporated into an electrical circuit which is responsive to the opening and closing of the circuit. For example, in one preferred embodiment, my invention may be very advantageously used in a power driven socket wrench wherein, when the design load in the member is reached an electrically conductive material is extruded from the member closing the circuit and shut-ting ofi the power. This arrangement is particularly advantageous in an assembly line operation. Also, the circuit could be wired in series to a battery and visual 3,383,961 Patented May 21, 1968 indicating means such as a light or an audio indicator such as a bell or horn could be used.

My wrench is primarily intended for cooperation with my improved stress indicating member, described generally in this application, and in greater detail in my copending companion application, Ser. No. 655,112, filed July 21, 1967.

Accordingly, my wrench may be placed over a fastening member which has been designed to indicate when a predetermined load has been reached by extruding an electrically conductive material. The member is tightened by the wrench until the design load is reached. This causes the member to extrude the electrically conducting material which touches a contact point in the wrench and closes an electrical circuit which emits a signal. With my invention, the wrenching means does not have to be removed to determine if the stress indicator has been actuated and the uncertainty of determining when the design load has been reached by checking structural changes visually or with instruments is avoided.

Brief description of the drawings.--FIG. 1 is a sectional front view of my invention;

FIG. 2 is an enlarged fragmentary view of a section of FIG. 1 after the nut has been tightened;

FIG. 3 is a sectional view of socket wrench engaged with a bolt head;

FIG. 4 is an enlarged fragmentary view of FIG. 3.

Description of the preferred emb0diments.-FIG. 1 shows a nut 10 such as described in my copending application Ser. No. 655,112, filed July 21, 1967, having an internal groove 12, and an external groove 14 between which grooves lies a shear section 16. The external groove is filled with an incompressible flowable electrically conducting material 18. The nut is secured to a bolt 20 and the shear section 16 is designed to yield plastically when the bolt has reached its design load, closing the external groove 14.

The nut is engaged by :a socket Wrench 22. Recessed in the wall of the socket wrench to prevent contacting the wall of the nut is a contact point 24. This point is adjacent the external groove 14 and connected by a wire 26 or other suitable conducting means to one side of an electric circuit (not shown). The wire may be insulated as shown by appropriate insulating material 32. The other side of the circuit is formed by the contact between the nut and the wall of the socket wrench and a wire 28 or other suitable means attached to the socket.

In operation, the wrench 22 is tightened and when the bolt reaches its design load the shear section 16 plastically deforms reducing the volume of the external groove 14 and extruding the electrically conducting material 18 as shown in FIG. 2. When the material 18 touches the contact point 24, the circuit is complete and a signal is emitted.

Another variation of my preferred embodiment is shown in FIGS. 3 and 4 in use with a bolt head such as disclosed in my copending application Ser. No. 655,112, filed July 21, 1967. FIG. 3 shows the socket wrench 22 engaged with the bolt head 34. The bolt has an internal groove 36 adjacent the abutting surface of the member 38 to be secured, and an external groove 40 filled with an electrically conducting incompressible flowable material 44. A shear section 42 lies between the grooves. The external groove is adjacent the contact point 24 which is tied into an electric circuit as previously described. When the bolt has been tightened to carry the load for which it was designed, the shear section 42 plastically deforming decreasing the volume of the external groove 40 and extruding the material 44. As shown in FIG. 4, the material touches the contact point 24 and closes the circuit as described before.

The material used in the external groove may be any electrically conducting flowable incompressible material such as polymeric material filled with iron filings and the like.

Although a socket wrench has been described and illustrated, it is obvious that my invention may be used with any type of wrenching means, such as, for example, a box wrench or open end wrench.

Also, it is to be understood that a wrench, such as a socket wrench, could be adapted to be electrically responsive to a nut or bolt which extrudes an electrically conducting material from the upper surface of the nut or bolt such as described in my copending application Ser. No. 655,112, filed July 21, 1967, which is hereby incorporated by reference in its entirety. That is the contact point in the wrench would be adjacent the upper su-rface of the nut or bolt.

My invention as described and illustrated avoids many of the difficulties associated in the past with indicating fasteners by providing a wrench which when engaged with a stress indicating fastening member electrically indicates when the design load has been reached, thus eliminating the need to remove the wrench periodically to make visual or mechanical inspections.

What I claim is:

1. A wrench electrically responsive to the deformation of a stress indicating fastening member which comprises:

(a) a jaw means;

(b) a surface within the jaw means for gripping engagement with the fastening member;

(c) at least one contact point disposed on the surface adjacent the fastening member and connected to an electrical circuit and positioned to be contacted by a material which is extruded from the fastening member to complete an electrical circuit when the stress indicating member deforms at its design load.

2. The wrench of claim 1 wherein the contact point is recessed within the surface.

3. The wrench of claim 1 wherein the wrench is a socket wrench.

4. The wrench of claim 1 wherein the wrench is a box type wrench.

5. The wrench of claim 1 wherein the wrench is an open end wrench.

6. The wrench of claim 1 wherein the material extruded from the fastening member is an electrically conductive material.

References Cited UNITED STATES PATENTS 2,857,793 10/1958 Peras 8l52.4 1,994,388 3/1935 Erichsen 73-14l 3,176,508 4/1965 Ward 73l41 2,503,141 4/1950 Stone 73141 JAMES L. JONES, ]R., Primary Examiner. 

